Image tube



July 26, 1960 R. G. STOUDENHEIMER ET AL 2,946,895

IMAGE TUBE Filed April 1, 1957 11v VEN TOR. R/GHARD a. STOI/DE/VHf/A/ERg yse/v/ c. 100/? i on the phosphor screen.

"i s State llVIAGE TUBE Filed Apr. 1, 1957, Ser. No. 649,777

7 Claims. (Cl. 250- 213) This invention relates to image tubes,particularly to improvements in so-called light-shutter tubes for use inhigh speed photography and has for its principal object to provide animproved gating and focusing electrode system for such tubes.

The foregoing and related objects are achieved, in accordance with theinvention, by the provision of a 2-electrode gating and focusing systemwherein the gating electrode (for passing or blocking theelectron-image) is of a special construction (later described) and ismounted close to the image cathode. The other or focusing electrodeoperates in conjunction with the gating electrode to focus the gated(i.e. passed) electron-image on a phosphor viewing screen. Deflectionplates are also provided for directing the focused electron-image to anyof different locations on the phosphor screen.

The invention is described in greater detail by reference showing thegating electrode of the tube.

In the drawings, an image tube 10 includes an envelope 12 which consistsof two hollow cylindrical glass portions 14 and 16 of substantiallyequal length and diameter.

The glass portions 14 and 16 are axially aligned and joined together bycylindrical metal rings 20 and 22 sealed to adjacent ends thereof. Atthe other end of Patented July 26, 19.60

a plurality of hollow cylindrical electrodes, for example, three coaxialelectrodes 44, 46, 48 of the same diameter and increasing length as theyprogress longitudinally from the photocathode. These electrodes arecoaxial with the tube envelope 12. The first cylindrical electrode 44 ispositioned close to the photocathode and is connected to the cathodecylinder 28. The second electrode 46 is positioned close to the firstelectrode 44 so that little or no space is provided between them so thatthe glass envelope is shielded. Second electrode 46 is electricallyconnected to a metal ring 50 sealed in the wall of the envelope 12.

A metal plate 51, oriented parallel to the photocathode and preferablyalso spherical in form and having substantially the same radius ofcurvature as the face plate 30 is secured to the end of the secondcylindrical electrode 46 which is adjacent to the tube face plate andis1 one end close to the second electrode 46 and with its the cylindricalglass portion 14 remote from the ring 20 is provided a cathode supportassembly 24. The cathode support assembly comprises an outer metal ring26 sealed to an inner metal ring 28 which comprises the cathodecylinder. A glass face plate 30, preferably spherical in form, is sealedacross the open portion of the outer ring 26 transverse to tube axis anda suitable electron emissive photocathode 32 is provided on the innerconcave surface of the face plate. The photocathode occupies a limitedarea at the center of the face plate 30. This area may conveniently havea diameter of about one inch. 7

At the end of the glass cylinder 16 remote from the rings 20 and 22 isprovided a phosphor screen assembly 34 which includes an inner ring 36sealed to an outer ring 38 and a generally flat glass plate 40 sealedacross the open portion of the outer ring. The glass plate 40 istransverse to the tube axis and has a diameter substantially equal tothat of the face plate 30. A suitable phosphor screen '42 is formed onthe inner surface of the flat glass 1 plate 40. An exhaust tubulation4,3 is provided in the envelope 12 closely adjacent to the photocathode32. Photographic film or the like may be provided outside of the tube 10in operative relation with the phosphor "for providing a convergentfield to focus an electron image This electrode system includes otherend connected to the ring 20. The end of the electrode 48 which isadjacent to the second electrode 46 is curved inwardly to shield theglass envelope 12 from materials evaporated during formation of thephotocathode 32. The electrodes '46 and '48 comprise the aforementioned2-electrode gating and focusing electrode system of the tube 10. 7

Between the third electrode 48 and the viewing screen 42 is provided ananode 5'2 which is preferably, but not necessarily, conical in form andincludes an apex 54 positioned just inside the adjacent end of thetln'rd electrode 48 at approximately the center of curvature of thephotocathode. The anode 52 also includes a base 56 positionedcloselyadjacent to the phosphor screen 42 and having a diameter substantiallyequal to that of the phosphor screen support plate 40. The apex 54 ofthe anode includes a short hollow cylinder 58 having a diameter which issmall compared to the diameter of the tube 10. The diameter of thisshort cylinder 58 may be of the order of one-quarter of the diameter ofthe tube 10-. Positioned directly behind the short cylinder 58 of theapex 54 is a metal plate 60 having a small central aperture 62 centeredon the axis of the tube 10 and defined by a longitudinally curved rimportion 64. The diameter of the aperture 62 is considerably smaller thanthat of the end of the short cylinder 58 which faces the photocathode.The base of the anode is welded or otherwise secured to the inner ring36 of the phosphor screen assembly 34 of the envelope.

A pair of electrostatic deflection plates 66 and 68 are mounted in thefield-free space within the anode and suitable leads 70 and 72 extendfrom the deflection plates and pass through and are insulated from thewall of the anode and are connected to pins 74 and 75 in the wall of theenvelope 12. The crossover point for electrons coming from thephotocathode is between the deflection plates near the apex 54 of theanode 52. This allows the deflection plates to be closely spaced andprovides maximum deflection sensitivity. In addition, since thedeflection plates 66 and 68 are positioned behind the metal 'plate 60which has the small aperture 62, the deflection plates cannot adverselyaffect the electrical focusing field between the apex of the anode andthe photocathode.

Metals to be evaporated for the formation of the photocathode 32, forexample antimony, silver, or the like, may be mounted in the form ofpellets 78 on electric heater wire 80 suitably connected to leads" (notshown) whereby heating current may be passed therethrough.Alternatively, these materials may be introduced by way of the exhausttabulation 43.

If cesium is used as a component of the photocathode, it is provided ina suitable container 79 mounted between the outer surface of thecylinder 46 and the inner surface of the envelope 12. This arrangementrestricts the deposition of cesium vapor to the region of thephotocathode. Cesium in the other parts of the tube is to be avoidedsince other electrodes should not be photosensitive. If other electrodeswere photosensitive, spurious photoemission would result which could notbe gated oft; by the electrode 46 which is the gating electrode of thetube 10. In addition, cesium on other electrodes and on the glassenvelope near electrodes operating at a high potential causes fieldemission which would hamper the operation of the tube.

Typical approximate dimensions for the tube 10 are as follows:

, Inches Overall length 10 Diameter 4 Length of electrode 44 A Length ofelectrode 46 1.5 Length of electrode 48 2.5 Length of anode 52 5Diameter of apex of anode 0.8 Radius of curvature of face plate 4Photocathode-to-gating electrode spacing 0.3

Typical operating voltages for the tube are as follows: Volts Anodesupply voltage 15,000 Electrode 48 3,000 Electrode 46 operating voltage190 to 210 Electrode 46 cut-off voltage -50 to l6 In operation of thetube, in order to gate the photocathode off, the gating electrode 46 isbiased at or beyond the cut-off voltage. The electrode 48 is, so tospeak, the operating partner of the gating electrode '46. It serves, inconjunction with the gating electrode, to focus the electron image onthe phosphor screen 42. To transmit an electron image from thephotocathode to the phosphor screen, the proper voltages are applied tothe other electrodes, the gating electrode 46 is pulsed to its positiveoperating voltage which gates the photocathode on. The electron image isthus allowed to pass along the tube toward the phosphor screen and thedeflection plates 66 and 68 are employed to position the electron imageat difierent locations on the phosphor screen. As the electron image isfocused at each position on the phosphor screen, the visible imageproduced is recorded on photographic film. Thus, a series of relatedpictures or frames may be produced. It can now be seen that the area ofthe photocathode depends on the desired number of frames to be formed onany single piece of photographic film with the selected size of phosphorscreen.

In constructing the tube 10, it is desirable that all corners inside theenvelope be smoothly rounded to avoid field emission. In addition, thearea of the photocathode may be varied depending on the desired size ofthe image on the phosphor screen.

The grid wires 55 should be as few as possible and as fine as possible.Three wires of the order of /2 mil in diameter have been found to besatisfactory in the tube described.

For all practical purposes, the speed of operation of the tube islimited by the pulsing circuit which is used to provide gating pulses tothe gating electrode 46. The tube 10 has been used to take pictures in atime as short as 10 second. in addition, with respect to pictureresolution, the tube 10 has resolution of about 22 to 30 lines per mm.With the dimensions given, the tube 10 may be used to provide fourpictures on the phosphor screen.

. V In the present invention, the provision of the Combi- 4, nation ofgating electrode and focusing electrode allows the voltages applied tothese electrodes to be balanced to provide optimum focus of a highquality electron image on the phosphor screen.

What is claimed is:

1. An image device comprising an electron-emissive photocathode adaptedto release an electron image in response to the impression of a lightimage thereon, a phosphor screen adapted to emit a light image inresponse to the impression of said electron image thereon in itsmovement along a path between said photocathode and said phosphorscreen, grid means surrounding said path and including an aperturedportion having a plurality of apertures, for gating said electron image,said path extending through said apertures, and means for focusing saidelectron image, on said phosphor screen.

2. An image device comprising an electron-emissive photocathode adaptedto release an electron image in response to the impression of a lightimage thereon, a phosphor screen adapted to emit a light image inresponse to the impression of said electron image thereon, said phosphorscreen and said photocathode forming a path for said electron image, a2-e1ectrode system surrounding said path for gating and focusing saidelectron image on said phosphor screen, and said gating system includingan apertured grid supported adjacent to said photocathode andsubstantially parallel to said photocathode.

3. An image tube comprising an electron-emissive photocathode adapted torelease an electron image in response to the impression of a light imagethereon, a phosphor screen adapted to emit a light image in response tothe impression of said electron image thereon in its movement along apath between said photocathode and said viewing screen, a 2-electrodesystem surrounding said path for gating and focusing said electron imageon said phosphor screen, said system including a first hollowcylindrical electrode having a grid positioned adjacent to andsubstantially parallel with said photocathode and a second hollowcylindrical electrode adjacent to said first electrode.

4. An image tube comprising an electron-emissive photocathode adapted torelease an electron image in response to the impression of a light imagethereon, a phosphor screen adapted to emit a light image in response tothe impression of said electron image thereon, said phosphor screen andsaid photocathode forming a path for said electron image, a 2-electrodesystem surrounding said path for gating and focusing said electron imageon said phosphor screen, said system including a first hollowcylindrical electrode having a closed-end including apertures positionedadjacent to said photocathode and a second hollow cylindrical electrodeadjacent to said first electrode, the apertured area of said closedendhaving substantially the same area as said photocathode.

5. An image tube comprising an electron-emissive photocathode adapted torelease an electron image in response to the .impression of a lightimage thereon, a phosphor screen adapted to emit a light image inresponse to the impression of said electron image thereon in its transitalong a path from said photocathode to said viewing screen, a2-electrode system adjacent to said path for gating and focusing saidelectron image on said phosphor screen, said system including a firsthollow cylindrical electrode having an apertured closed-end positionedadjacent to said photocathode and adapted to gate the photocathode onand off, and a second hollow cylindrical electrode adjacent to saidfirst electrode, the aperture in said closed-end being spanned by aplurality of spaced wires and being aligned with said photocathode andhaving substantially the same area as said photocathode.

6. An image tube comprising an electron-emissive photocathode adapted torelease an electron image in response to the impression of a light imagethereon; a phosphor screen adapted to emit a light image in response tothe impression of said electron image thereon; an anode electrode infront of said phosphor screen; said photocathode and said phosphorscreen providing the ends of a path for said electron image through saidtube, a 2-electrode system adjacent to a portion of said path for gatingand focusing said electron image on said phosphor screen, said systemincluding a first hollow cylindrical electrode having an aperturedclosed-end positioned adjacent to said photocathode and a second hollowcylindrical electrode adjacent to said first electrode; and a pair ofdeflection plates disposed within said anode, the crossover point forelectrons from said photocathode being between said deflection plates.

7. An image tube comprising an electron-emissive photocathode adapted torelease an electron image in response to the impression of a light imagethereon; a phosphor screen adapted to emit a light image in response tothe impression of said electron image thereon; said photocathode andsaid phosphor screen forming a path for said electron image through saidtube, a 2-e1ectrode system positioned around a portion of said path forgating and focusing said electron image on said phos phor screen, saidsystem including a first hollow cylindrical electrode having anapertured closed-end positioned adjacent to said photocathode and asecond hollow cylindrical electrode adjacent to said first electrode; agenerally conical anode electrode having an apex disposed within saidsecond hollow electrode and a base positioned adjacent to said viewingscreen; and a pair of deflection plates mounted within said anode nearthe apex thereof and at the crossover point for electrons from saidphotocathode.

References Cited in the file of this patent UNITED STATES PATENTS2,322,361 Iams June 22, 1943 2,421,182 Bayne May 27, 1947 2,666,864Longini Jan. 19, 1954 2,683,816 Bouwers July 13, 1954 2,692,341 Schagenet 'al Oct. 19, 1954 2,839,601 Fries June 17, 1958 FOREIGN PATENTS709,192 Great Britain May 19, 1954

